Hello Paddypaws, and welcome to the forum!
It is always exciting to have a bumblebee nest in your garden - even if it can be a bit inconvenient! I have a nest in my compost bin - so cannot take out any compost, or even add to it, as this causes a lot of frantic buzzing!
The nest will naturally die in the autumn - exactly when depends on where you are in the UK, and how successful the nest is. So, if you can wait until then to replace your shed, that might be easiest?
If you need to exchange sheds before then, there is helpful advice on the BBCT website about moving a bumblebee nest, which might help - ie if you could do the change over after dark, when the bees are less active. Again, this depends on where you live - if you are in the far north of Scotland, I don’t know if it gets dark enough at this time of year.
With regards to identification, your lovely photo looks like the abdomen of a buff-tailed bumblebee worker, but the thorax would usually have a yellow stripe. If you submit the photo to BeeWatch, you will get an identification, if you don’t get one from the forum. See what other replies you get!
Thank you for the advice. I’ve decided to leave the bees well alone until the nest naturally comes to an end. I’ll put my new shed up then. They do seem to get quite cross when I go to near their nest so relocating it I don’t feel is an option. I’ll just enjoy watching their activity from a safe distance and leave my garden makeover until Autumn.